A sample size of 90 subjects produces two-sided 95% CI with the following width: when the sample proportion of patients with an HIV-1 viral load < 50 copies/mL is between 40% and 60%, the 95% CI width is 0.2, that correspond to the possible maximum width in this study. Corresponding widths are 0.17 for a sample proportion of 0.30 (or 0.70), 0.15 for a sample proportion of 0.20 (or 0.80) and 0.13 for a sample proportion of 0.10 (or 0.90) (PASS 11. NCSS, LLC. Kaysville, Utah, USA).